NASA Scientific and Technical Aerospace Reports

Hydrodynamic film-riding gas seal, having been successfully used in industrial pump and compressor applications for
decades, is now finding way into aero-engines. Aerospace applications require the seal work robustly under various speeds and
constantly changing pressures. Maintaining seal face flatness is also more challenging in aerospace than in industrial
applications because of the seal size and the rapid thermal transition in aero-engines. Another difficulty in aerospace
application comes from the altitude condition, where air is thin, not enough opening force may be generated to separate the
seal faces from touching. Therefore, the hydrodynamic groove design is more critical in aerospace application. In order to
maximize the seal performances, the groove shape and depth are optimized for the worst application condition, such as at the
altitude, with using a 2D model coupled with a non-linear optimization procedure. Seals designed in this way have been found
working well both in rig test and in on-flight evaluation. However, two recently designed seals based on full optimization were
found not working during rig test. These two seals features very fine grooves that is thinner than the other seals that worked
well. The 2D code from time to time predicted that seals work better if more grooves were engraved. The under-performed
two seals indicated there might be something missing in the 2D model. It was speculated that the entrance losses and 3D effects
for narrow grooves become significant, resulting in reduction of hydrodynamic opening force. In order to quantify the
influences of 3D effect, a three-dimensional model is therefore developed to calculate the fluid flow between the seal faces,
and then the results are compared with the 2D solution. The model solves a circumferential section of seal face that consists
one land and one groove region. A small region outside the sealing face is also included to simulate the flow entrance and exit.
It was found that the 3D CFD model generally agrees with the 2D model in determining the optimum groove dimensions. The
3D code gives similar trend predictions of seal opening force under the influences of groove depth, number of grooves, land
to groove ratio and groove angle, although there exist differences in the absolute value levels. The 3D CFD results forced a
re-examination of hardware and further re-test the seal. It is concluded that the problems were due to manufacture tolerance
with such fine grooves. The design code is correct, but manufacture capability should be incorporated. CFD results and test
data are reported in this paper.
Author
Computational Fluid Dynamics; Sealing; Two Dimensional Models; Three Dimensional Models; Fluid Flow; Aerospace
Engineering
20060002385 Advanced Products Co., CT, USA
High-Temperature Metallic Seal Development for Aero Propulsion and Gas Turbine Applications
More, Greg; Datta, Amit; 2004 NASA Seal/Secondary Air System Workshop, Volume 1; October 2005, pp. 1-18; In English;
See also 20060002371; Original contains color illustrations; No Copyright; Avail.: CASI: A03, Hardcopy
An innovative seal consisting of a blade alloy spring energizer and cold formable superalloy jacket can be designed for
applications above 1500 F. The seal is expected to minimize cooling air and leakage thereby enhancing engine efficiency. The
design can be further improved with cast net shape single crystal springs attached to an easily machinable superalloy ring. The
single crystal spring structure can also be used where low load/ high deflection device is required for extremely high
temperature applications.
Derived from text
High Temperature; Seals (Stoppers); Loads (Forces); Leakage; Heat Resistant Alloys; Crystal Structure; Single Crystals
20060002461 Lawrence Livermore National Lab., Livermore, CA USA
Dimensional Measurements of Three Tubes by Computed Tomography
Schneberk, D. J.; Martz, H. E.; Brown, W. D.; Oct. 13, 2004; 12 pp.; In English
Report No.(s): DE2005-15014597; UCRL-TR-207195; No Copyright; Avail.: Department of Energy Information Bridge
Low density polyethylene (LDPE), copper (Cu), and gold (Au) tubes were scanned on KCAT to identify and evaluate the
impact of phase effects on quantitative object recovery. These tubes are phantoms for high energy density capsules. Digital
radiographs for each tube are shown in Figure 1. The LDPE tube was scanned at 60 kV, while the Cu and the Au tubes were
scanned at 140 kV. All tubes were scanned at a magnification of 3, with approximately 100-mm distance between the exit plane
of the tube and the scintillator. Notice the prominence of the outer bright and inner dark edges for the LDPE tube DR, and
their absence from the Cu and Au tube DRs. The bright and dark edges are a result of change in phase of the x-rays. The x-ray
fluence is partly attenuated and partly refracted. The location near the outer edge of the tube appears to be more attenuating
since those x-rays have refracted to locations just outside the tube. Alternatively, the added counts from the refraction result
in intensities that are greater than the incident intensity effectively representing a negative attenuation. This results in more
counts in that location than in the incident intensity image violating the positivedefinite requirement for standard CT
reconstruction methodologies. One aspect of our CT processing techniques remove some of this signal on the outside of the
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